The first Tablets were made by G-d, like the body of writing as explained in the Torah. The latter Tablets were made by man [Moses], as it says “Carve for yourself two stone tablets.” (Exodus 34:1) Tablets are things which cause standing and existence, that it’s not “letters fluttering in the air.” Since they were made by Hashem, they would stand eternally. But the second ones, which were man-made, only exist subject to conditions and constraints.

היינו דהלוחות הראשונים היו מעשה אלקים כמו גוף הכתב כמו שמפורש בתורה, והלוחות האחרונים היו מעשה ידי אדם כמה שכתוב “פסל לך שני לוחות אבנים”, וענין הלוחות הוא דבר המעמיד ומקיים שלא יהיו אותיות פורחות באויר, וכיון שהיו מעשה ה׳ היה עומד לעד, אבל השניות שהיו מעשה אדם אינם מתקיימים רק בתנאים וגדרים,

When Rav Shimon speaks of “letters fluttering in the air”, he is using an idiom our sages used describe the destruction of the first Tablets. When Moses came down the mountain and the Jews were worshiping the Golden Calf, the letters fluttered up to heaven, and the tablets became heavy, and Moses threw them down. (Tanchuma, Ki Sisa 30; Exodus Rabba 46:1)

The same expression also appears in a description of R’ Chanina ben Tradiyon’s martyrdom. He was wrapped in a Torah, which was set aflame. He was packed with wet wool, so as to prolong his suffering. His students asked him, “Rebbe, what do you see?” He replied, “The parchment is burning, but the letters are fluttering in the air.” (Avodah Zara 18a)

Also possibly relevant is the idiom’s use in contract law, describing the paper or parchment of a contract as a critical component; for example, if the husband refuses to relinquish ownership of the paper, his writ of divorce is invalid, merely “letters fluttering in the air.” (Gittin 20b) The writing surface is an essential element of the text, it is what gives the sequence of letters their permanence.

The difference between the luchos is who prepared the writing surface — Hashem Himself carved out the first ones, but Moshe had to provide the sapphire upon which Hashem wrote the second luchos. Because the writing surface denotes permanence, this explains why someone who studied Torah the first, divinely carved luchos, would never forget what he studied.

There is a famous dispute between Rabbi Eliezer and Rabbi Aqiva about what it is we commemorate with the mitzvah of sukkah.  The Torah reads (Vayiqra 23:42-43):

בַּסֻּכֹּ֥ת תֵּֽשְׁב֖וּ שִׁבְעַ֣ת יָמִ֑ים כָּל־הָֽאֶזְרָח֙ בְּיִשְׂרָאֵ֔ל יֵֽשְׁב֖וּ בַּסֻּכֹּֽת: לְמַעַן֮ יֵֽדְע֣וּ דֹרֹֽתֵיכֶם֒ כִּ֣י בַסֻּכּ֗וֹת הוֹשַׁ֨בְתִּי֙ אֶת־בְּנֵ֣י יִשְׂרָאֵ֔ל בְּהֽוֹצִיאִ֥י אוֹתָ֖ם מֵאֶ֣רֶץ מִצְרָ֑יִם אֲנִ֖י יְהוָ֥ה אֱלֹֽהֵיכֶֽם׃

You shall dwell in sukkos for seven days; every native in Israel shall dwell in sukkos. So that your generations will know that I made the Israelites dwell in sukkos when I took them out of the Land of Egypt; I am Hashem your G-d.

The gemara (Sukkah 11b) records the dispute:

ענני כבוד היו דברי ר’ אליעזר ר”ע אומר סוכות ממש עשו להם

“They were clouds of glory,” these are the words of Rabbi Eliezer. Rabbi Aqiva says, “They made themselves actual booths.”

Among commentators on the verse, Rashi follows Rabbi Eliezer, that “I made the Israelites dwell” refers to the clouds of glory. Ramban quotes Rashi, and agrees. Rashbam and Ibn Ezra, on the other hand, focus on the word “basukkos – in sukkos” and understand the literal meaning of the verse to follow Rabbi Aqiva’s mention of physical booths.

In general, aggadic disputes are not decided by the rules of halachic pesaq. Here, however, the dispute has halachic outcome — the verse relays a halachic rule whether through its literal meaning or through a midrashic one. The Torah obligates us to sit in the sukkah “so that the generations will know.” At least lekhat-chilah (ab initio) one needs to have intent, to use the sukkah as a reminder of something. And therefore, which is it? Are we to sit in the sukkah and contemplate the sukkos our ancestors built in the desert, or to remember the clouds of glory Hashem provided us with?

The Tur, Shulchan Arukh, and Arukh haShulchan (Orach Chaim 525) side with Rabbi Eliezer, and we are told we sit in the sukkah to commemorate the clouds of glory. (My apologies to the rationalists.)

Why is Sukkos in the fall?

The aforementioned Tur says it’s so that we make it clear that we are sitting in the sukkah for the mitzvah, and not because it’s a comfortable way to spend a spring or summer day. (I’m not sure that in practice the underlying assumption holds for Israel’s climate.)

The Vilna Gaon gives an answer I found to be more profound, and related to the above dispute. When the Jews left Egypt, we were surrounded by clouds of glory. These clouds departed with the Golden Calf. After the Golden Calf, Moshe went up on the mountain for 40 days to obtain forgiveness for the Jewish People, and another forty days to get a second set of luchos. He returned with the second luchos on Yom Kippur, which is much of why the 10th of Tishrei is Yom Kippur.

On the 11th, Moshe instructed us about building the Mishkan. During the next couple of days people brought their donations, and on the 14th of Tishrei, Moshe had to tell them to stop — that they had everything needed.

So, as our sages compute is, on the 15th of Tishrei, the actual assembly of the Mishkan began. And, the Vilna Gaon notes, the clouds returned. What we commemorate by sitting in our sukkos is not the initial gift, but the return of the clouds after Yom Kippur.

The first luchos differ from the second luchos in a similar way to the distinction we just made with respect to the clouds of glory. The first set were like the clouds, given as a gift to the Jewish People with no effort on our part. The second required that Moshe make the preparatory step. And similarly, the clouds of glory returned after that same Yom Kippur on which we received the second luchos, but not until people took a step by themselves. We first started assembling the Mishkan and only then did Hashem respond by providing the protecting clouds.

Viewed at this level, the Vilna Gaon provides a partial synthesis of the positions of Rabbi Eliezer and Rabbi Aqiva. Yes, we sit the sukkah to remember Hashem providing clouds that protected us. However, those clouds did not come on their own — they were in response to the human effort Rabbi Aqiva places primary. The dispute then becomes whether we are to remember clouds obtained by the religious effort or physical walls we erected manually — and provided protection also because of our trust in the Almighty. But the notion of gifted protection is not part of either.

Yom Kippur was a renewal of the covenant based on the terms that we must take the first step, and Hashem responds.

In the case of aquiring Torah, we have to refine the writing surface through improving our middos and then study, and Hashem will grant us success.